WO2001067434A1 - Active noise reduction system - Google Patents
Active noise reduction system Download PDFInfo
- Publication number
- WO2001067434A1 WO2001067434A1 PCT/NZ2001/000037 NZ0100037W WO0167434A1 WO 2001067434 A1 WO2001067434 A1 WO 2001067434A1 NZ 0100037 W NZ0100037 W NZ 0100037W WO 0167434 A1 WO0167434 A1 WO 0167434A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- noise
- sound
- signal
- analogue
- acoustic
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1785—Methods, e.g. algorithms; Devices
- G10K11/17853—Methods, e.g. algorithms; Devices of the filter
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1787—General system configurations
- G10K11/17875—General system configurations using an error signal without a reference signal, e.g. pure feedback
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1787—General system configurations
- G10K11/17885—General system configurations additionally using a desired external signal, e.g. pass-through audio such as music or speech
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/30—Means
- G10K2210/321—Physical
- G10K2210/3217—Collocated sensor and cancelling actuator, e.g. "virtual earth" designs
Definitions
- This invention relates to active noise reduction systems.
- one of the fundamental problems with insulators or absorbing materials is that they do not work well at reducing noise at the low frequencies. This is primarily because the acoustic wavelength at low frequencies becomes large compared to the thickness of typical absorbent materials.
- Active noise reduction can overcome these problems and disadvantages.
- Active noise reduction is based on the principle of superposition of signals. According to the principle of superposition, if two signals exist, one an undesired disturbance, the other a controlled response, their combined effect can be made zero if they are equal in magnitude and opposite in phase. This signal cancellation phenomenon is commonly termed destructive interference, and is a basis for the operation of active noise reduction systems.
- Active noise reduction exploits the long wavelengths associated with low frequency sound. Active noise reduction systems are, therefore, more effective at attenuating low frequency acoustic disturbances. Such low frequency disturbances are the common undesired side effect of operating machinery and are difficult to reduce using passive techniques.
- active noise reduction systems typically comprise small and light weight components. This means that active noise reduction systems can be used in many situations where passive methods are impractical due to their bulk, weight and cost effectiveness.
- Active noise reduction systems based on the known adaptive feedforward techniques, for example, can experience problems with effective parameter convergence and therefore provide less than optimal performance.
- Adaptive techniques also require intensive processing particularly where the feedforward path dynamics are complex and the time available to compute a control response is brief. In many cases this makes this method of control unfeasible due to cost or the inability to implement the system practically.
- the invention may broadly be said to consist in an active noise reduction apparatus including:
- a sensing means provided in the sound field for providing an input signal corresponding to sound from the sound source means and noise in the sound field
- a processing means including
- noise signal estimation means for producing a noise estimate being an estimate of a component of the input signal corresponding to the noise
- an inversion means for processing the noise estimate to produce an output signal which is used to drive the sound source means, and whereby
- the sound source means provides sound in the sound field which is of substantially equal amplitude and opposite phase to the noise in the sound field thereby substantially reducing the noise by destructive interference.
- the noise signal estimation means includes a model of the open loop dynamics of the apparatus and the output signal is applied to the model to provide an estimate of the input signal which is substantially devoid of the noise component.
- the apparatus further includes algebraic adding means to add the estimated input signal which is substantially devoid of the noise component to the input signal to derive an estimate of the noise component.
- the invention may broadly be said to consist in an active noise reducing control method, the method comprising the steps of sensing sound in a sound field, the sound including sound produced from a sound source means provided in the sound field, and noise in the sound field, providing at least an estimated noise component being an estimate of a component of the sensed sound corresponding to the noise,
- the invention may broadly be said to consist in an active noise reduction system having a sensing means to sense sound produced by a sound source in a sound field, and noise in the noise field,
- the inverted replica of the sensed noise being provided to a second fixed point digital filter having means to compensate for the undesirable dynamic effect of the physical components comprising the system
- the output of the second digital filter being provided to the sound source whereby the sound source unit processes the signal to produce sound in the sound field which substantially destructively interferes with the noise in the sound field.
- the invention may broadly be said to consist in an open loop active noise reduction system according to any one of the preceding statements of invention.
- the invention may broadly be said to consist in a feedforward control method for an active noise reduction system according to any one of the preceding statements of invention.
- the invention resides in an active noise reduction system that utilises a digital filter to obtain a signal indicative of the noise desired to be reduced by the system, and to invert the noise signal to formulate a controlling acoustic response which when combined with the acoustic noise at a position of control error measurement results in a substantial cancellation of both signals via the mechanism of the destructive interference of signals.
- the fixed point digital filter outputs to an acoustic actuator a compensated estimate of the inverted acoustic noise signal present at a measurement and control position.
- the compensation effected is an accurate and stable inversion of the active noise reduction system's open-loop dynamics, that is, the dynamics of the combined system components located between the output and input terminals of the active noise reduction electronic circuitry.
- the active noise reduction system preferably comprises one or more acoustic actuator(s), active noise reduction electronic circuitry required to physically implement the fixed point digital filter, and one or more acoustic sensor(s).
- the digital component of the active noise reduction electronic circuitry preferably comprises one or more digital-signal-processors (DSP), one or more analogue-to-digital (ADC) converters and one-or more digital-to-analogue converters (DAC).
- DSP digital-signal-processors
- ADC analogue-to-digital converters
- DAC digital-to-analogue converters
- the analogue component of the active noise reduction electronic circuitry preferably comprises on the input side a preamplifier and on the output side a power amplifier.
- the digital sampling frequency selected is high enough such that the level of acoustic signal present at frequencies equal to or greater than the Nyquist frequency falls well below the noise floor of the analogue-to-digital converter so as to eliminate any need for anti-aliasing filtering.
- the digital sampling frequency selected is high enough to eliminate any need for reconstruction filtering.
- analogue-to-digital converters and digital-to-analogue converters used at the input and output of the digital-signal-processor respectively exhibit a very low group delay.
- the DSP, ADC and DAC devices are embodied in one piece of silicon known as a mixed-mode application-specific-integrated-circuit (ASIC) to minimise processing latency, reduce the phase-lag gradient and improve noise reduction performance.
- ASIC application-specific-integrated-circuit
- a distance separating the acoustic actuator and sensor is set as low as possible to reduce the phase-lag gradient of the open-loop system and improve noise reduction , performance. More preferably the distance between the acoustic actuator and acoustic sensor is zero.
- a simple analogue feedback compensator augments the DSP, deriving signal from' the acoustic sensor and outputting to the acoustic actuator and to the DSP via an ADC to yield a hybrid digital-analogue active noise reduction implementation.
- analogue feedback compensatory dynamics are designed to cancel any remaining low frequency noise.
- an analogue controller comprising a cascaded network of phase-lag and/or low pass filters.
- a programme audio reference is.input.to the DSP via an ADC and is output as part of the. acoustic control response. This reference signal is not cancelled during any noise cancellation.
- Figure 1 is a schematic of the configuration of components, comprising the system of the invention.
- Figure 2 is a block diagram of the system of Figure 1.
- Figure 3 is a diagram of a practical implementation of the system of Figure 1.
- Figure 4 is a schematic of the system of Figure 1 but with a programme audio reference included.
- Figure 5 is a block diagram of the system of Figure 4.
- Figure 6 is a diagram of a practical implementation of the system of Figure 4.
- Figure 7 is a schematic of the system of Figure 1 but with a programme audio reference and analogue feedback compensator included.
- Figure 8 is a block diagram of the system of Figure 7.
- Figure 9 is a diagram of a practical implementation of the system of Figure 7.
- Figure 10 is an illustration of the invention embodied as an active headset device providing noise cancellation within the ear piece.
- Figure 11 is an illustration of the invention embodied as an active panel device providing cancellation near and around the panel.
- Figure 12 is a perspective view of further active panel device according to the invention.
- the acoustic sensor (10) with associated components such as cables and connectors (12) is represented as block S(s) in the block diagrams.
- the active noise reduction electronics shown in the schematic diagrams incorporates the analogue input electronics (14), the digital-signal-processor and the analogue-to-digital and digital-to-analogue converters (16), and the analogue output electronics (22).
- the acoustic actuator (24), with associated components such as cables and connectors (13), is shown as block A(s) in the block di-fgrams.
- a digital filter determines an appropriate control effort, W D (/ 7) (20) (designated U D (Z) in the block diagrams) based on the measured and sampled control error signal, e m (kT), (17) (designated E m (z) in the block diagrams) according to the following control law,
- u D (kT) C D2 (z)*u O (kT) + C D1 (zYe m (kT) (lb)
- C DI (Z) and ⁇ 2 (z) represent the filter parameters in the complex frequency domain
- uj)(kT) represents the vector of n current and past values of control effort according to
- e m (kT) represents the vector of m current and past values of measured and sampled error according to ⁇ e m (kT), e m ((k-l)T), e m ((k- 2)T) e m (k-m)T) ⁇ , C ⁇ (z) and m denotes the number of order of C D I(Z).
- the control error, ⁇ (t), is the summation of the acoustic control response, y(t), (18 and designated 7(5) in the block diagrams) and the acoustic noise, n(t), (19 and designated N(s) in the block diagrams), at the predefined position of control and measurement, or,
- the measured control error, e m (t), (21 and designated E m (s) in the block diagrams) is the control error, e(t), (16 and designated as E(s) in the block diagrams), processed by the acoustic sensor, S(s) according to,
- y m (kT) denotes the sampled measured acoustic control response
- n m (kT) denotes the sampled measured acoustic noise. Both y m (kT) and n m (kT) can not be directly measured.
- y(t) when reaching this position, must closely match the inversion of the acoustic noise, or -n(t). For the sampled data stream, therefore, y m (kT) must closely match -n m (kT).
- n ' m (kT) e m (kT) - z M'(zYviv(kT) (5)
- M'( ⁇ ) represents a discrete time model of the open loop dynamics of the combined system components of the plant, or
- A(s) (24 in the block diagrams) and P(s) (25 in the block diagrams) represent the dynamics of the acoustic actuator and acoustic path respectively.
- M'(z) is determined using accurate spectral analysis. For example, a high resolution frequency-response-function of the system between the input to A(s) and the output of S(s) can be measured. An inverse Fourier transform of this complex data will yield an accurate finite-impulse response (FIR) filter representation of M(s).
- FIR finite-impulse response
- this signal is processed by a filter FO(z), representing an accurate and stable inverse of M(s), in terms of both phase and magnitude, according to,
- M'(z) When M'(z) is obtained in FIR form preferably 0(z) is calculated by employing optimal or robust signal processing techniques. For example, M'(z) maybe transformed into an equivalent state-variable representation where an optimal and fully recursive filter, 0(z), maybe determined by using linear-quadratic-regulator (LQR) design techniques.
- LQR linear-quadratic-regulator
- This equation is implemented physically in the time domain by using a DSP device of sufficient power to process this filter at the selected sampling frequency 1/T.
- the sampling frequency selected is high enough such that the level of acoustic signal present at frequencies equal to or greater than the Nyquist frequency falls well below the noise floor of the analogue-to-digital converter so as to eliminate any need for anti-aliasing filtering.
- the sampling frequency selected is high enough to eliminate any need for reconstruction filtering.
- the DSP has as its input the measured and sampled control error, e m (kT), that is provided by an ADC device.
- the ADC is connected, via auxiliary analogue electronics and associated cabling (12), to the acoustic sensor (10).
- the digital fixed point filter processed in the DSP outputs a stream of control effort values, Uoik ), to a DAC device where it is transformed into an analogue continuous signal and then transmitted to the acoustic actuator (24) via some auxiliary analogue electronics (22) and associated cabling (13).
- the control effort is converted into an acoustic response and it then passes to the measurement position (10) via the acoustic path where on arrival it is termed the acoustic control response and ideally combines with the acoustic noise to provide significant acoustic noise reduction.
- the DSP, ADC and DAC devices are embodied in one piece of silicon known as a mixed-mode application-specific-integrated-circuit (ASIC) to minimise processing latency, reduce the phase-lag gradient and improve noise reduction performance.
- ASIC application-specific-integrated-circuit
- the filter parameters, C DI (Z) and C D2 (Z) are preferably stored on a memory device within the active noise reduction system's electronic circuitry. These parameters would be loaded to the DSP device on booting. Alternatively they maybe stored external to the electronic circuitry but downloaded to it by a cable or other electronic means.
- the schematic shows provision of an analogue program audio reference to the system.
- the analogue reference signal is processed by the processing section (16) so as to be provided as an audio signal to the actuator (24) together with the necessary signal to provided noise cancellation at the sensor (10).
- the reference signal, represented as R(s) is added to the analogue driving signal provided to the actuator (24).
- R(s) is also processed to provided a digital signal which is added to the digital control effort for provision to the open loop plant estimation and is thus compensated for by the system so that the correct inversion of the estimated noise is provided to the optimal inversion filter.
- FIG. 6 a practical implementation is illustrated showing the reference signal in digital form, r(kT), being added to the control effort to thereby be provided to the acoustic path or sound field. Therefore, a reference signal corresponding to sounds such as music may be provided to the acoustic path and will appear to a listener in the vicinity of the sensor (10) to be substantially free of background noise.
- the reference signal could also correspond to a signal from a public address system for example.
- the program audio reference signal is shown provided to an analogue feedback compensator (15) which augments the digital signal processor to yield a hybrid digital-analogue active noise reduction implementation.
- the analogue feedback compensatory dynamics are designed to cancel any remaining low frequency noise.
- the compensation is achieved by a cascaded network of phase-lag or low pass filters.
- the block diagram shows the analogue control effort produced by the analogue feedback compensator (15) being subtracted from the reference signal and the result added to the analogue output of the digital control effort.
- the digital processing circuitry compensates for this by adding a digital form of the analogue control effort to the digital control effort provided to the open loop plant estimation to thereby provide a compenstaed inverted noise estimation.
- the system is embodied as an active headset (30).
- The. acoustic sensor (32) used here is an electret-condenser microphone (ECM).
- ECM electret-condenser microphone
- the microphone detects the control error at the measurement position and passes this to the active noise reduction system's electronic circuitry (34).
- the control effort is computed according to the developed control law and is acoustically output via a mylar speaker actuator (36).
- the acoustic control response and noise signals combine providing active noise cancellation within the region bounded by the earpiece (38) of the headset device and the wearer's ear (not shown).
- the system is embodied as an active panel loudspeaker system (40).
- the acoustic sensor (42) used here is an electret-condenser microphone (ECM).
- ECM electret-condenser microphone
- the microphone detects the control error at the measurement position and passes this to the active noise reduction system's electronic circuitry (44).
- the control effort is computed according to the developed control law. It is then acoustically output via an electromechanical transducer (46) to the flat panel diaphragm (48).
- the acoustic control response and noise signals combine providing active noise cancellation in a zone near the measurement position.
- FIG 12 a further flat or planar loudspeaker (50) incorporating noise cancellation apparatus according to one or more of the examples discussed above.
- the planar loudspeaker (50) has a diaphragm (52) on which there is located a microphone (54) which detects ambient noise. Ambient noise detected by the microphone (54) is sent to the noise cancelling circuitry (now shown). The noise cancelling circuitry then produces a cancellation signal as discussed above, which is then sent to the transducer (56) which causes the speaker panel and diaphragm to vibrate, thereby producing sound.
- the acoustic control response and noise signals combine providing active noise reduction in a zone in the vicinity of the loudspeaker.
- a speaker of this type may be used in a variety of applications and asserted to being provided in the walls of rooms, or in parts of seat head rests, telephone phone booths or the like where it may be highly desirable to have a zone of silence.
- the dimensions of such a speaker and the relatively small size of the circuitry for noise suppression as set forth above create a highly desirable compact system which therefore has significant advantages over relatively more bulky and complex prior art constructions.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2001565169A JP2003532913A (en) | 2000-03-07 | 2001-03-07 | Active noise reduction system |
AU2001244888A AU2001244888A1 (en) | 2000-03-07 | 2001-03-07 | Active noise reduction system |
EP01918015A EP1297523A1 (en) | 2000-03-07 | 2001-03-07 | Active noise reduction system |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NZ50322100 | 2000-03-07 | ||
NZ503221 | 2000-03-07 | ||
NZ503242 | 2000-03-08 | ||
NZ50324200 | 2000-03-08 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2001067434A1 true WO2001067434A1 (en) | 2001-09-13 |
Family
ID=26652161
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/NZ2001/000037 WO2001067434A1 (en) | 2000-03-07 | 2001-03-07 | Active noise reduction system |
Country Status (6)
Country | Link |
---|---|
US (1) | US20010036283A1 (en) |
EP (1) | EP1297523A1 (en) |
JP (1) | JP2003532913A (en) |
CN (1) | CN1427988A (en) |
AU (1) | AU2001244888A1 (en) |
WO (1) | WO2001067434A1 (en) |
Cited By (3)
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JP2006526921A (en) * | 2003-06-02 | 2006-11-24 | フェオニック ピーエルシー | Audio system |
CN103905959A (en) * | 2012-12-26 | 2014-07-02 | 上海航空电器有限公司 | Active noise control device based on pilot headset |
EP2551845B1 (en) * | 2011-07-26 | 2020-04-01 | Harman Becker Automotive Systems GmbH | Noise reducing sound reproduction |
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US20100284546A1 (en) * | 2005-08-18 | 2010-11-11 | Debrunner Victor | Active noise control algorithm that requires no secondary path identification based on the SPR property |
US9025638B2 (en) * | 2004-06-16 | 2015-05-05 | Telefonaktiebolaget L M Ericsson (Publ) | Method and apparatus to compensate for receiver frequency error in noise estimation processing |
CN1812293B (en) * | 2005-01-26 | 2011-05-04 | 乐金电子(中国)研究开发中心有限公司 | Time division multiplexing access noise controlling system and method used for GSM mobile telephone |
CN1851804B (en) * | 2006-05-22 | 2010-07-07 | 南京大学 | Active soft boundary acoustic shielding |
FR2906389B1 (en) * | 2006-09-21 | 2008-12-26 | Neopost Technologies Sa | REDUCED NOISE LEVEL MAIL PROCESSING MACHINE |
CN101393736B (en) * | 2008-10-28 | 2011-03-30 | 南京大学 | Active noise control method without secondary channel modeling |
US9020158B2 (en) | 2008-11-20 | 2015-04-28 | Harman International Industries, Incorporated | Quiet zone control system |
US8135140B2 (en) | 2008-11-20 | 2012-03-13 | Harman International Industries, Incorporated | System for active noise control with audio signal compensation |
US8718289B2 (en) | 2009-01-12 | 2014-05-06 | Harman International Industries, Incorporated | System for active noise control with parallel adaptive filter configuration |
US8189799B2 (en) | 2009-04-09 | 2012-05-29 | Harman International Industries, Incorporated | System for active noise control based on audio system output |
US8199924B2 (en) | 2009-04-17 | 2012-06-12 | Harman International Industries, Incorporated | System for active noise control with an infinite impulse response filter |
EP2549774B1 (en) * | 2009-04-28 | 2020-09-02 | Bose Corporation | Method of operating a dynamically configurable ANR circuit and apparatus therefor |
US8077873B2 (en) | 2009-05-14 | 2011-12-13 | Harman International Industries, Incorporated | System for active noise control with adaptive speaker selection |
EP2259250A1 (en) * | 2009-06-03 | 2010-12-08 | Nxp B.V. | Hybrid active noise reduction device for reducing environmental noise, method for determining an operational parameter of a hybrid active noise reduction device, and program element |
DE202009009804U1 (en) * | 2009-07-17 | 2009-10-29 | Sennheiser Electronic Gmbh & Co. Kg | Headset and handset |
DE102010039017B4 (en) * | 2010-08-06 | 2017-09-21 | Robert Bosch Gmbh | Method and device for active damping of an acoustic transducer |
CN102332260A (en) * | 2011-05-30 | 2012-01-25 | 南京大学 | One-piece signal channel feedback ANC system |
US8824695B2 (en) * | 2011-10-03 | 2014-09-02 | Bose Corporation | Instability detection and avoidance in a feedback system |
CN103077703B (en) * | 2012-12-25 | 2014-12-24 | 桂林电子科技大学 | Method and device for inhibiting dynamic noise |
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- 2001-03-07 JP JP2001565169A patent/JP2003532913A/en active Pending
- 2001-03-07 EP EP01918015A patent/EP1297523A1/en not_active Withdrawn
- 2001-03-07 US US09/799,714 patent/US20010036283A1/en not_active Abandoned
- 2001-03-07 CN CN01809100A patent/CN1427988A/en active Pending
- 2001-03-07 WO PCT/NZ2001/000037 patent/WO2001067434A1/en active Application Filing
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JP2006526921A (en) * | 2003-06-02 | 2006-11-24 | フェオニック ピーエルシー | Audio system |
EP2551845B1 (en) * | 2011-07-26 | 2020-04-01 | Harman Becker Automotive Systems GmbH | Noise reducing sound reproduction |
CN103905959A (en) * | 2012-12-26 | 2014-07-02 | 上海航空电器有限公司 | Active noise control device based on pilot headset |
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JP2003532913A (en) | 2003-11-05 |
US20010036283A1 (en) | 2001-11-01 |
EP1297523A1 (en) | 2003-04-02 |
CN1427988A (en) | 2003-07-02 |
AU2001244888A1 (en) | 2001-09-17 |
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